1. Field of the Invention
The present invention relates to a document search system capable of performing an associative search by correlating a plurality of document databases and to a search server.
2. Description of the Related Art
With a progress in the electronic description of document information, a request has been made for a highly accurate document search technology for targeting a plurality of document databases different in kind. There has also been an increase in request for investigation as to correlation of a group of documents among the plurality of document databases. For example, many requests are made for a search of related items in an encyclopedia regarding interesting newspaper articles.
A currently practiced keyword search system can search a plurality of document databases by switching them. However, for a group of documents in a certain document database, it is impossible to search a group of documents related thereto from the same document database or another document database (a search system referred to as a document associative search).
Limited in the same document database, pre-calculation of a degree of correlation between documents enables a document associative search for searching and entering a group of documents related thereto to be realized. However, for a plurality of document databases, such a document associative search is, accompanied with an increase in the number of document databases, practically impossible because of an explosive increase in the number of combinations regarding the degree of correlation between documents to be pre-calculated.
On the other hand, Japanese Patent Laid-Open No. 2000-155758, entitled “DOCUMENT SEARCH METHOD AND DOCUMENT SEARCH SERVICE TARGERING PLURALITY OF DOCUMENT DATABASES”, discloses a method of efficiently searching a group of documents from an optional document database, the group of documents being correlated to an optional group of documents in a document database specified by a user. According to the method disclosed therein, a high-speed document associative search is realized by using only, as a summary for search, characteristic words in a search input, which is entered as the group of documents. This method enables a user to execute a highly accurate and efficient document search by investigating correlation between the groups of documents while switching a plurality of document databases different in kind.
A search client of a document search server capable of performing an associative search by correlating a plurality of document databases has a mechanism for selecting a document database to be searched. The user carries out a search by selecting a document database to be searched from a document database list. Generally, a showing order of the list of selectable document databases is fixed. When a document database to be searched by the user was shown below in the list, the time and work of selection caused a reduction in convenience for the user. To enhance the user convenience, the ordering of the document databases must be changed according to a use state of the user.
A search server having the document databases registered therein generally collects registration fees and commissions from owners thereof. In many cases, the registration fee is fixed or set according to the number of times of accessing the document database. The commission is levied on a part of a profit obtained by the owner of the document database. Generally, a part of a subscription that the user pays to the owner of the document database is paid as a commission.
To calculate the registration fee or the commission, the document database must be evaluated. In the conventional keyword search server, the number of times of accessing the document database has typically been used. However, in an associative search server, there are factors, which make it impossible to perform an evaluation based on only the number of accessing times. For example, it is assumed that the registration fee of a document database enjoying a wide subscription is reduced while that of a document database enjoying a limited subscription is increased. If there is a document database frequently used as source articles for an associative search, because of its limited subscription, an evaluation of this document database is poor, consequently increasing a registration fee. However, since this document database is used as source articles for the associative search, it contributes to an increase in an activity level of the entire associative search server, which should be highly evaluated. In other words, only the use of the number of accessing times is not enough for the evaluation of the document database, and it is necessary to evaluate, by a proper measure, a contribution made to the activity level of the entire associative search server.